Generally, the threshold current of semiconductor lasers depends strongly on the ambient temperature, or the temperature of the laser. Usually, the threshold current increases with increasing ambient temperature. Therefore, in most optical communication systems the lasers are cooled by a thermolectric cooler. In some systems the laser driver is constructed with the capability to change the biasing point to compensate for any changes in the threshold current.
All of the countermeasures utilized to compensate for increasing threshold current with increasing ambient temperature greatly increase the cost of the optical system. In low cost optical interconnects it is preferable to have a direct drive laser without additional devices such as thermolectric coolers, etc. For such applications, the temperature sensitivity of the semiconductor laser is very important.